1. Field of the Invention
This invention relates to hand-operated mechanisms for closing and opening heavy doors and to counterbalanced door assemblies incorporating such mechanisms. The invention is particularly suited for use with heavy counterbalanced doors found in floors, sidewalks and roofs that are horizontally hinged and need to be pulled closed from below. The invention is designed to provide the mechanical advantage needed to overcome friction and move the mass of a large counterbalanced door with a single hand.
2. Description of Related Art
Horizontally hinged doors are commonly used in sidewalks, in the floors of industrial facilities for access to subterranean locations and for roof access in large buildings. Doors of this type are often made of metal, typically steel or aluminum, and due to their weight they are normally counterbalanced for safety and ease of operation.
Quite often such a door will have a fixed ladder mounted below the door. When a user is descending the ladder and desires to close the overhead door, he must be able to do so with one hand while holding onto the ladder with the other hand. In such applications it is desirable to reduce the force that needs to be exerted on the closing handle to close the door.
It is particularly desirable to reduce the force needed on the handle at the initial portion of the door's motion. During this portion of the door swing, the user must pull on the handle at an angle from the ladder which tends to pull him away from the ladder. Moreover, a greater closing force needs to be exerted on the handle at the start of the swing to overcome the hold-open forces of inertia, friction and counterbalancing than is needed to continue the closing motion after the door is moving.
At the other end of the door swing, as the door nears the closed position, the user is pulling down parallel to the ladder. This is relatively easy as the user can use his weight to assist in closing the door.
The prior art has attempted to alleviate problems in closing the door from below by counterbalancing and reducing the friction of the door. A door that is well counterbalanced throughout its swing and that is designed to operate with low friction will decrease the level of closing force needed throughout the swing of the door.
However, often it is not desirable, or for cost reasons it is not feasible, to reduce the friction to near zero or to exactly counterbalance the door throughout its range. For example, in some applications it is desirable to have sufficient friction that the door stays in position when it is released at a midpoint in its swing. In other applications the counterbalancing system may be designed to provide some extra counterbalancing force at the top to ensure that the door will move to the fully open position when released near that position. A slight extra force may also be generated at the top of the swing to hold the door open, however, most doors are mechanically retained in the fully open position so that they will not close inadvertently.
For these reasons, it is preferable to increase the mechanical advantage of the hand-operated closing system provided at the initial portion of the door swing.
Accordingly, it is one object of the present invention to provide a counterbalanced door assembly with a door closing mechanism that can be easily operated with one hand.
It is another object of the invention to provide a counterbalanced door assembly with a door closing mechanism that can be operated by a user on a ladder.
It is yet another object of this invention to provide a counterbalanced door assembly where the initial force required to begin moving the door towards the closed position is reduced as compared to prior art doors.